A Planet Candidate on a 4.35-day Orbit around the Active K Dwarf TIC 257484419

Version 2 of a preprint on an unconfirmed planet candidate around the active K dwarf TIC 257484419 (Gaia DR3 5149427640557882368, 80 pc, candidate member of the 120 Myr Pisces-Eridanus stream). A transit-like signal of depth about 1.1 ppt recurs every 4.353304 days. It was flagged by the SPOC pipeline in TESS sector 97 and had no TOI, CTOI or published designation. The ephemeris derived from sectors 30 and 97 places transits in sector 3 (2018), and a dip is found there in six full-frame-image reductions. If the signal is planetary, the radius is about 2.5 Earth radii. Odd and even transits agree, no secondary eclipse is seen, a difference-image analysis and Gaia astrometry place the source within about 2 arcseconds of the target, and Gaia radial velocities exclude a close stellar companion. TRICERATOPS gives a false-positive probability of 0.085 to 0.103, dominated by the possibility of a planet around an unresolved bound companion, and about 0.1 per cent for all eclipsing-binary and blend scenarios. The candidate is not confirmed. The star is active, its Gaia astrometry leaves room for a companion (RUWE 1.32), and the age and stream membership have not been checked spectroscopically. A blind search of a single sector is close to the detection limit set by the stellar noise, so the evidence rests on the signal recurring at the predicted times in three sectors; the paper gives the injection-recovery and random-phase tests. High-resolution imaging and radial-velocity follow-up are needed. Predicted mid-transit times for sector 108 (September to October 2026) are included as a test (first published in version 1 on 3 October 2026, before the data were released). What changed from version 1: the paper was rewritten in a standard article structure (introduction, host star, data and methods, results, discussion, references); new tests were added (red-noise-calibrated significance of the recurrence, injection-recovery, a kinematic membership check, and a test of which star hosts the transit); the false-positive discussion was corrected; and references were checked and completed.